The invention relates to hydraulic fracture monitoring methods and particularly relates to determining the dimensions of the fractures resulting from hydraulic fracturing of a formation and may be applied in oil and gas fields.
Formation hydraulic fracturing is a well-known method to stimulate hydrocarbons production from a well. During a formation fracturing job a highly viscous liquid (also known as a fracturing fluid) containing a proppant is injected into the formation in order to create a fracture in a production zone and fill the created fracture with the proppant. To ensure efficient use the fracture must be located inside the production zone and not protrude into the adjacent strata as well as have sufficient length and width. Therefore, a fracture dimensions determination is a critical stage to ensure fracture process optimization.
Currently a fracture geometry is determined using various technologies and methods. Best known are the methods (so-called fracturing imaging), ensuring assessment of spatial orientation of the fracture and its length during the fracturing job and are mostly based on localization of seismic events using passive acoustic emissions. This localization is ensured by the “cloud” of acoustic events, leading to a volume within which the fracture may be positioned. These acoustic emissions are microseisms resulting from either high pre-fracture stress concentration, or a decrease of the current stress around the fracture with the subsequent fracturing fluid flowing into the formation. At best these events are analyzed to obtain information about the source mechanism (energy, displacement field, stress drop, source dimensions etc.). Analyzing the results of these events, it is impossible to obtain direct quantitative information concerning the main fracture. Other methods are based on measuring the deformation of the earth using tiltmeters either from a surface or from a wellbore. All these methods are rather expensive due to the necessity of proper positioning of the sensors in an appropriate location with good mechanical coupling between the formation and measurement tools. Other methods ensure an approximate assessment of the fracture height based either on temperature variations or on the data obtained using isotopic tracers (tracer atoms). A review of the aforementioned imaging methods above is presented, e.g., in the following publication: Barree R. D., Fisher M. K. Woodroof R. A. (2002), “A practical Guide to Hydraulic Fracture Diagnostic Technologies”, SPE, paper 77442, presented at Annual Technological Conference and Exhibition in San Antonio, Tex., Sep. 29-Oct. 2, 2002.
The closest prior art is a method for hydraulic fracture dimensions determination, described in the USSR Certificate of Authorship No. 1298376, 1987. This method provides for injection of a fracturing fluid under pressure into a well bore, enabling the said fluid to create fractures near the well and to penetrate into them and further through the fracture surfaces into a formation filtration zone around the fractures. Then fluid flow parameters are measured. A disadvantage of this method is the necessity to use additional equipment and complicated calculations.
The purpose of the claimed invention is the creation of a method for determination of the dimensions of a fracture resulting from hydraulic fracturing activities based on the analysis and simulation of the fracturing fluid pumping out after the fracturing.